Process of eliminating internal stresses in wire at anchorages thereof



Jan. 6, 1931. A. v. DE FOREST PROCESS OF ELIMINATING INTERNAL STRESSESIN WIRE AT ANCHORAGES THEREOF Filed Feb. 17, 1928 INVENTOR Alfred Mdefbrest FUN/ ATTORNEY V Patented Jan. 6, 1931 im1-En {STAT-ES P ENT FF f{I I1 I AI REnv. ron'nsr, or s'rnn'rronco, ooNNEcr'IcUnAssIeNoR ToAMERiGAN 01mm Y a COMPANY, 'mc;, CORPORATION OFVNEW YoRx' xraoonss orELIMINATING INTERNAL STRESSES IN wInn'm ANorronAGEs 'rxmmior Applicationfiled February 17, 1928. Serial No. 255,153.

The present invention relates to a process of eliminating lnternalstresses" in wire tension members which are looped around an anchorageor an attachment member. I I

5Aspecific applicationof the present invention is to be found in thecables of suspension bridges. ,It is customary to form such cables of anumber of strands, each strand being formed of acontinuous wire which iscarried by a trolley back and forth from, anchorage to anchorage untilthe desired number of wireleng ths for a strand have been spun. Eachwire length is subjected to tens on as soon as it is spun and isthenlooped about an anchorage shoe. WVhen the strand-has been completed,the anchorage shoe is inserted between a pair of eye bars or otheranchorage means and, attached there- J to, after which it is drawnbackby anysuit able meanssuch asanhydraulic jack toadjust the strand asa whole tension or sag. I

However, internal stresses are introduced into the wire by bending itaround an anchorage shoe, which stresses are by no means negligible evenincold drawn wire and which,

in the case of heat-treated wire, are so'serious as to preclude the useof heat-treated metal .1

for the tension members of ;suspension bridges.

ticity and high yield point as compared with cold worked products. Whensuch wire is bentaround relatively small diameters such as theshoe atthe anchorage of the suspen-r sion bridge, avery high, stress isintroduced v by thisrbending in the outside fibres of the I p I I amountof heat treatment to eliminate :the;

- wire, If, as would usually be the case, this It is an-object of thepresentinvention to prevent any accumulation of a stress at the bend inthe wire and. reduce the load on the wire atxthis point to the samefigureas that inthe straight portions of the wire.

to a predetermined a ties of; the

The essential f-quality of heattreated. metal, is its high modulus ofelasnow be described in connection with the ac- A more specific objectof the invention is to subject the wire toatforming operation, whichpermanentlystretches the outside fibres and permanentlycoinpresses theinside fibres .so that the forces across any section will be zero, asthey are in the straight portionofwire. In" other words, althou lithewire is bent, the bending. The curved portion may then be loaded by anyload which does notchange its radiusof curvature without introducin anyother than the same tensile forces which operate, on the straightportions leading .to the curve. L f a 1' .Anotherobject of the inventionis to subject the wire to over-stressing whereby its elasticlimit willbe temporarily lowered so that, it'may be subjectedftoa considerableamount of deformation and after this deforination an aging effect willtake place which will-intimerestore the full elasticproperwire; Itiswell known that heatt-reat ed steel mayliave its elastic limits temeit is not under stress ueto;

porarily lowered byjsubjecting the material effect.

Anotherobj ect ofthe invention is to sub ject the-looped wires of thestrand to heat 7 treatment afterthe strand, as a whole, has

beensubjectedto,finaltension, so as to elimi 1 nate any internalstresses which may still be present the members ofthestran'd.

S till another object is to apply a protective metallic coating on theloop: end of the strand, this'coating being applied inmolten condition;at a; temperature that will insure a certain internal stresseswhich may:be present in the wire and tofhasten the aging effect which willrestore the wire to its full elastic prop; ertiesr ,g yq

With these andother objects in view. which will appear hereinafter, theinventionwill companying drawings 7 and thereafter the novelty and scopeof the--invention will be, pointed outintheclaims f r c.

flInthedravvirigs,: t, l l Fig. 1 'sa somewhat'diagrammatical plan itakes place which restores the full elastic treat se over which the wireis bent is of no particular importance and there is no danger ofweakness due to inexactness of the location of the tangent between thestrain portion of the wire andthe beginning of the curvature. After" theloop has been formed, an aging process properties to the wire. 7

Fig. 3 shows still another. method oftem. porarily reducing the elasticlimit of that portion of the wire which is to be looped about theanchorage shoe. On the anchorage shoe 10 is mounted a form 30, such as apulley, about which an incoming wire is bent. The

. wire after passing about the form 30, is attached to a tension means31, such as a block and tackle, by which the wire may be drawn up to thedesired preliminarytension so that it will lie parallel to other wiresin the strand. The diameter of the form 30 is such that the wire onbeing drawn thereabout is bent beyond its elastic limit to such anextent as to take a fixed curvature corresponding to the curvature ofthe shoe 10. After the wire has been given this curvature,it is held invadvance of the form 30 by the clamp to main- 'tain said preliminarytension in the main body of the wire While tensioning means 31 isreleased. The curved portion of the wire is then transferred to the shoe10.

The length of wire sub'ected to the bending process by drawing it a outthe form is considerably greater than the length of the curved portionof the shoe about which the wire loop is to be fitted. It is necessary,therelbre, to eliminate the curvature in that part of the wire whichextends beyond the curved part of the shoe. This is done by passing thewire, after it leaves the form 30, in a re verse bend about a secondform 32, also,

mounted on the anchor shoe. The form 32 is so located with respect toform 30 that the length of wire from the point at which it begins tobend about the pulley '30 to the point at which it begins to bend aboutthe form 32 equals'the length of the curved part'of the shoe. The curvethus formed in the wire corresponds not only to the curvature of theshoe 1 butalso to the length of said curvature. Fur. thermore the pulley30 is so positioned that the wire will becurved in the proper locationto coincidewith the curved part of the shoe.

Fig. 4 shows the shoe turned at right. angles to the position shown inthe plan views Figs. 1, 2 and 3 and secured between a pair of eye bolts33 by which the shoe is seizedand drawn backwardjto subject the strandas a whole to the requisite tension. A stud 34: passes through the. eyebolts and also through the opening'12 in the shoe. After the shoe hasbeen secured to the eye bolts, a metallic shield 35 is fitted around theshoe over the strand loop. The shoe'and strand loopfare then heated andmolten'plead is poured intothe peripheral recess of theshoearound thewires ture andfintroduced in such quantit iasto raisethe;temperature'ofthe strand 00 to approximately 800 degrees Fahrenheit, w ich temperatureis suflicient to draw the temper of the wires so that'if there be anyinternal stresses therein'they willbe dissipat'e'd. The lead filli-nthus serves not only "to coat the wires at Ens point andprotect themfrom; rust, but also to bind them all together and to heat-treat them,so as to eliminate objecti onal internal 1 "stresses. After this, thestrand may'besubjected to the necessary tensionby drawing on the eyebolts 33 so as to raise the strand to the predetermined sag of thefinishedcable. Y *VVhile' particular reference has been made hereintothe application of the present in ventionfto bridge strands andcables, and'to highte'nsile hqeat-treated wire, obviously the inventionis not limited to such wire nor to such application, but can be usedinthe loop-- i'n-g of'any tensioninember inrod or,wire. form and inwhich it is desirable to eliminate internal stresses. .7 i Having thusdescribed my invention, what lclainr and'desire to protect by LettersPatentis:"* In the process-of forming a stress-free anchorage loop inhigh tensile wire,the steps which comprise progressively subjecting aportion'of the wire to reverse flexing beyond its elastic limit, andsimultaneously bending suchporti'on ofth'e wire toform a loop havingapermanent set of predetermined curvature' 2. Infthe process of forminga stress-free anchorage loop-in high tensile wire, the steps" v1nareverse bend about a secondform.

j "In the process of spinning bridge cables of high tensile wire, thesteps which compriseprogressi-vely'subjecting a portion of the wire toreverse flexingbeyondits yield" point, sil multaneously bending- F'suchportion of the wire into a loophaving a permanent set of Y predeterminedcurvature, and transferring the loop thus formed to an anchorage.

4. In the process of spinning bridge cables of high tensile wire, thesteps which comprise drawing the .wire under tension in'one directionabout. a form to progressively bend the wire beyond its elastic limit,drawing the wire in the opposite direction about another form toeliminate, from a portion of the wire, the I curvature produced bybending the wire around the first form, and fitting the remain-' ingcurved portion of the wire about an. anchorage. i

5. In the process of spinning bridge cables of high tensile wire, thesteps which comprise bending a portion of each length of Wire into a*loop;jaapplyin gmolten metal ab'out the loops thus-formed,smaintainingthe metal at a predetermined temperaturesufiicient to; :relieve internalstress and artificially age the wires A and allowing the metaltosolidify about the wire-loops,

- i V I .-.6. ln tlieprocess ofispinning -bridge cablesof'high-tensile;wire,-the steps-which'comprise bending-a portion of.each length of wire beyondits elasticlimitintofa loop of suchjdimensions thahwhen released the loop will assu'me a fixed form ofpredetermined curvature,transfer;ring each loopthus formed to ananchorage; applying molten metal about i the;loops 'n aintaining:themetalat aprede' terminedtemperature sufficienttozrelieve interna-lstress and. artificially age the: Wires,

' and allowing themetal to solidify about the wire loops. v 7 .7 d 1 .77. Inthe process of spinning bridge cables of high tensile-wire, thesteps which comprise bending a portion of each length of wirebeyo'nd itselastic limit into a'loop of such dimansions thatgwhen released" theloop will a assume a fixed form of predetermined curvatnre, transferringeach loop thus formed to an anchorage, vpreheating thewi re loops,applying molten metal about the loops and anchorage, maintaining themetal at a predetor-mined temperature suflicient to relieveinternal-stress and artificially ageithe wires, and" allowingthe metaltosolidify about the loops} and anchorage. v V 8 In the process ofanchoring high tensile wire, the} steps which comprisesubjectingthe wireto a predetermined tension and simul tan'eou'sly drawing aportion of'thewire about a-form ofsucl diameter asto bend the-wire beyondits elasticlimit and give the wire a prede'termined fixed curvature, drawing thewire-in a reverse bendabout a second form tostraightena portion of thewire curved by drawing it about the first form, and fittingf theremaining curved. portion or the wire 1 about ananohorage, 'cIn-1testimony whereof, I have signed this o specification;

LALFREIj n F EST, I

